Vast numbers of people travel every day via aircraft, trains, buses, and other vehicles. Such vehicles are often provided with components that are important for passenger comfort and satisfaction. For example, passenger aircraft (both commercial and private aircraft) can have catering equipment, heating/cooling systems, lavatories, water heaters, power seats or beds, passenger entertainment units, lighting systems, and other components, which require electrical power for their activation and proper operation. These components are generally referred to as “non-essential” equipment. This is because the components are separate from the “essential” equipment, which includes the electrical components required to run the aircraft (i.e., the navigation system, fuel gauges, flight controls, and hydraulic systems).
One ongoing issue with these components is their energy consumption. As non-essential equipment systems become more and more numerous, they require more and more power. Additionally, because more equipment components are converted to electrically powered equipment (rather that hydraulically or mechanically powered equipment), power availability can become a concern aboard aircrafts. These systems are typically powered by power drawn from the aircraft engines drive generators (although they may derive power from an aircraft auxiliary power unit or ground power unit when the aircraft is on the ground.). However, the use of aircraft power produces noise and CO2 emissions, both of which are desirably reduced. The total energy consumption can also be rather large, particularly for long flights with hundreds of passengers on board.
The technology of fuel cell systems provides a promising, cleaner, and quieter way to supplement energy sources already aboard commercial aircraft. A fuel cell system produces electrical energy as a main product by combining a fuel source of liquid, gaseous, or solid hydrogen with a source of oxygen, such as oxygen in the air, compressed oxygen, or chemical oxygen generation. Fuel cell systems consume hydrogen (H2) and oxygen (O2) to produce electric power. The H2 and O2 gas may be provided via gas distribution systems that generally include high pressure cylinders for storing the gases.
Fuel cell systems are generally designed with two in-line pressure regulators on both gas distribution systems (H2 and O2) in order to expand gases from the high pressure storage cylinders to the low pressure inlets (the appropriate fuel cell inlet pressure for the H2 and O2 gases). The anode and cathode pressure of the fuel cell system should be linked in order to limit the pressure differential between the two fuel cell inlet pressures (anode and cathode) so as to avoid damaging of the fuel cell membrane.
Whenever hydrogen or other potentially explosive gas is in use, there are regulations to be met. For example, the ATEX directive consists of two European directives that outline requirements for what equipment and work environment is allowed in an environment with a potentially explosive atmosphere. (ATEX derives its name from the French title of the 94/9/EC directive: Appareils destinés à être utilisés en ATmosphères EXplosibles.) Fuel cell systems typically need to use ATEX actuators and sensors, and otherwise be ATEX compliant. This disclosure relates to improvements for fuel cell systems that allow them to be ATEX compliant, while reducing the total number of required compliant components and limiting the portions of the fuel cell systems where compliant components are required. This disclosure also relates to improvements for fuel cell systems that allow the fuel cell system to operate autonomously. The fuel cell systems may operate without requiring power from the aircraft. The fuel cell systems may also be designed to operate without requiring a power converter.